Optical mixing of plan position indication and graphical information

ABSTRACT

649,322. Radio navigation ; radio relaying systems. MARCONI&#39;S WIRELESS TELEGRAPH CO., Ltd. July 30, 1946, No. 22734. Convention date, July 31, 1945. [Classes 40 (v) and 40 (vii)] In a radio navigation system the P.P.I. view of craft (ships or aircraft) within the service area of a ground located P.P.I. system is radiated as a signal by a ground located transmitter and displayed on a television receiver carried by each craft. As shown in Fig. 1, the view on the long persistence screen 26 of a cathoderay tube forming part of a P.P.I. system including a rotatable directive aerial 10, a pulse transmitter 11, T-R box 12 and pulse receivers 13, 13a, is scanned by a conventional television camera 28 together with a chart 34 of the surrounding territory and the resulting television signals are transmitted on frequency f3 by the transmitter 33. To receive these signals each craft (e.g. aircraft A/C1, A/C2) is provided with a television receiver 41, Fig. 3, operating on the frequency f3 and the received television signals are displayed on the screen 50 of cathode-ray tube 48 a device coupling the deflection yoke 49 to a directional gyro being provided for maintaining a desired orientation of the received P.P.I. display. Identification of the echo which corresponds to a particular aircraft may be effected by providing each aircraft with a responder, such as 42, comprising a pulse receiver 57 delay network 58 and pulse transmitter 59 (operating on frequency f2) the output from which is increased by closing a switch 55 so that the brightness of the particular echo is increased. In an alternative identification method demodulated pulses from the responder receiver 57 are applied to an integration circuit 62 and the resulting pulse (e.g. pulse 56, which is the integrated energy of the group of pulses received by 57 as the P.P.I. beam sweeps past of the aircraft) is applied to the grid of cathode-ray tube 48 to increase the brightness of the echo. If it is desired to operate the P.P.I. receiver at such a low gain that a rotating strobe line (e.g. due to noise signals) is not visible, means are provided to introduce a strobe line that is always visible regardless of the receiver gain setting. As shown in Fig. 5, a rotating strobe line 98, obtained by illuminating a slit 101 in a disc which is rotated in synchronism with the deflecting yoke 17, is projected on to the chart 34 and television signals representative of this display generated by a camera 96 and mixed in 97 with signals representative of the P.P.I. display generated by camera 28 are radiated by the television transmitter 33. The system is preferably operated with relative amplitudes of modulation so that the strobe line only produces a visible trace on the screen of the airborne television receiver when the identification pulse 56 is operative, the P.P.I. display producing maximum and the chart an intermediate degree of modulation. If the P.P.I. tube screen is made of phosphorescent material having a persistence of one or two minutes the resulting &#34; trail &#34; produced by the echo signals will indicate the direction of movement of the objects producing these echos. If the aircraft are not equipped with responders (operating on frequency f2) the echo signals produced by reflection from the surface of the aircraft may be utilized by providing the P.P.I. system with a receiver operating on the frequency of the pulse transmitter (e.g. f1). In an embodiment of the invention in which an aircraft flying at a certain altitude receives at any one time a picture containing only aircraft flying at the same level, or at any one of other predetermined levels, the P.P.I. ground installation is equipped with a plurality of television receiver-transmitter systems, each system of which operates on frequencies assigned to a particular level, the receivers and transmitters each being tuned to different carrier frequencies and the frequencies of the responder transmitter and the television receiver carried by the aircraft are adjusted automatically (by means of an altitude operated tuning mechanism such as 91, 93, 94, Fig. 3) to the assigned frequency as the altitude at which the aircraft is flying varies (Fig. 4, not shown).

May 2, 1950 H. c. ALLEN OPTICAL MIXING OF PLAN POSITION INDICATION AND GRAPHICAL INFORMATION Filed April 50, 1948 6157' I 7 rmwmme/e 5 17 7 X r r v I C/IMER/I 3 Y 11 Patented May 2, 1950 OPTICAL MIXING OF PLAN POSITION INDI- CATION AND GRAPHICAL INFORMATION Horace Clifford Allen, Princeton, N. 5., assignor to Radio Corporation of America, a corporation of Delaware Application April 30, 1948, Serial No. 24,136

2 Claims. 1

This invention relates to improvements in position indicator systems and more particularly to visual indicators as used for radio traffic control systems of the type wherein the positions of mobile craft such as aircraft within a service area are determined by radar equipment providing a visual map-like display, said display being relayed, together with other pertinent visual information such as a map, by television to the various aircraft concerned. A traffic control system of said type is described and claimed in co-pending U. S. patent application Serial No. 607,999, filed July 31, 1945, by L. F. Jones, now abandoned, entitled Improvement in system of air navigation.

One of the principal objects of the present invention is to provide improved methods and means for optical mixing of visual information from different sources, for transmission as a whole over a single television channel in the form of superimposed images. For example, in traffic control systems of the above-mentioned type, it is desirable to send a map superimposed on the radar positional display, and perhaps written instructions or other visual information as well. Accordingly, it is one of the specific objects of this invention to provide improved methods and means for optically superimposing such other visual information upon a radar display, for transmission by television.

Since it may be desirable from time to time to alter the written instructions or other graphical information in the composite display which is transmitted by television, it is necessary to provide a writing surface, either upon the map or upon some other support, where it is accessible to an operator or controller. A further object of the invention is to provide an improved writing surface particularly adapted for use with a television camera.

Another object is to provide systems of the described type including means which enables the operator or controller to see the composite picture in its relationship to the surface upon which he is writing or about to write, thus facilitating accurate and rapid writing or marking on said surface.

It will be evident to those skilled in the art that the light produced by a, radar display is expensive light, in that its production involves the use of special luminescent materials and carefully regulated high unidirectional voltage, while light produced by common illuminants such as incandescent or fluorescent lamps is relatively cheap. Accordingly, it is desirable not to waste the light from the radar display, and it is one of the objects of this invention to provide optical mixing of the described type with a minimum loss of said light.

The foregoing and perhaps other objects of the invention will be apparent upon consideration of the following description with reference to the accompanying drawings, wherein:

Figure 1 is a schematic diagram of a relatively simple embodiment of certain features of the invention in an optical mixing arrangement for traffic control systems of the type described in the above-mentioned Jones application,

Figure 2 is a schematic diagram of a preferred modification of the system of Figure 1, and

Figure 3 is a schematic diagram of a further modification of the system of Figure 1.

Referring to Figure 1, a radar set I of known type is provided with a position indicator including a cathode ray oscilloscope 3 which is .controlled by output signals from the radar set to show the positions of reflecting objects, such as aircraft, as luminous spots or pips. The single line 5 represents all of the various connections between the radar set I and the oscilloscope 3,

including conductors for the intensity and deflection control signals. For purpose of explanation of the invention, it may be assumed that the arrangement is such that the oscilloscope 3 provides a so-called P. P. I. or plan position indication, wherein the luminous spots represent the positions of corresponding objects as viewed from directly above the radar station.

A television camera I, also of known type, is focussed on the screen of the indicator 3 and supplies output signals to a television transmitter 9. The single line I l represents the several conductors required to supply deflection signals to the camera, as well as to carry video signals from the camera to the transmitter. Similarly, the line l3 represents the necessary conductors leading to an oscilloscope l5 which is to be used as a monitor and display the picture represented by the signals which modulate the transmitter 9.

A partially reflecting mirror H is provided between the indicator 3 and the camera I, and a surface l9 supporting'a map or the like is arranged so that its image isreflected by the mirror H to the camera 7. In the illustrated arrangement, the distance from the surface I9 to the camera, by way of the mirror l1, must be made the same as that from the indicator 3 to the camera, in order that both will appear to lie in the same plane as viewed by the camera. It will be evident, however, that the two distances may be made unequal providing a. proper arrangement of lenses is included between the camera and the oscilloscope and/or the surface I9. A light source 2| is provided for illuminating the surface [9.

In the operation of the system of Figure 1, the radar set 1 functions in known manner to produce a P. P. I. display on the face of the tube 3, representing the positions of aircraft within the service area as luminous spots. A substantial portion of the light from the radar display passes through the reflector IT. The camera 1 picks up the radar display and provides corresponding video signals. v

The map or other graphical representation on the surface It is illuminated by the light source 2|. Some of the light from the map is reflected by the mirror ll and the reflected image appears to the camera to be superimposed upon the radar display. The video output from the camera thus represents both the map and the P. P. I. picture. The scale of the map, and its position and orienta tion, are made to conform with the P. P. 1. picture, so the composite television picture will show the aircraft as spots at corresponding positions on the map.

The video signal corresponding to the composite picture modulates the television transmitter 9 for broadcasting to all properly equipped aircraft in the vicinity. The video signal also operates the monitor oscilloscope l5, producing thereon a display like that to be reproduced on board the aircraft. An operator or controller may inscribe on the map information or instructions, such as lines representing wind direction and speed,icourses to be followed, or written information, such as weather reports. The inscribed material will appear in the composite television picture as broadcast, and can be observed by the operator at the monitor tube l5.

As mentioned before, light produced by the oscilloscope tube 3 is expensive and must be utilized as efflciently as possible. Hence it is desirable to design the reflector I! to transmit say 70 percent or moreof the light from the tube 3. The cost of lighting the map surface It is also not to be ignored, because it is viewed by reflected light and may require that the source 2| be very intense. When the mirror I! is a more or less panchromatic reflector, such as a partially silvered sheet of glass, a compromise must be effected between the amount of light lost in transmission and the amount lost in reflection.

In accordance with present invention, the mirror ll is a dichroic reflector, comprising a transparent sheet coated with a thin layer of material having a refractive index different from that of the sheet. Such mirrors are well known in the optical art, and can be designed to transmit 80 percent or more of incident light of one color, while reflecting 80 percent or more of incident light of another color.

The phosphor on the screen of the tube 3 may be one of the highly efiicient types, emitting predominantly blue light, for example. The mirror I? is designed to transmit blue, and will reflect efficiently some other color, such as orange. The

' light source 2| may be an incandescent lamp,

which provides substantial output in the yelloworange region of the spectrum, or may be a specially designed fluorescent lamp.

'With this'arrangement substantially all of the available light from the tube 3 will reach the camera 1, and at the same time a minimum of loss will occur in the transfer of light from the support l9 to the camera. Since the camera pick-up tube can be made to respond well to both blue and orange, the difference in color of the two images will have little effect. In this connection, it should be noted that the above-mentioned colors are given only by way of example; other colors, or even invisible light such as. ultra-violet or infrared could be used.

The operator, in marking on the map, must watch the monitor tube It: to see the relationship between the marks he is making and the positions of the various pips in the radar display. This may be somewhat diflicult because the monitor and the map surface cannot be seen simultaneously, and the operator must look from one to the other.

The foregoing difficulty is avoided in the system of Figure 2, wherein a marking stylus 23 is mechanically coupled, as indicated schematically by the dash line 25, to a pointer 21 which is manual- 1y movable over the face of the monitor tube 15. The mechanical connection 25 may be a pantograph arrangement, a telautograph, or any other well-known system for moving the stylus 23 in accordance withthe motions of the pointer 21.

Although an opaque surface could be used as in the system of Figure l, the writing surface illustrated in Figure 2 is a flat transparent sheet 29, illuminated from below by a source 3| and covered on top with an opaque coating 38 which can be removed by a cutting or scraping action of the stylus 23. The writing surface is projected by a lens upon the photosensitive target of a television pick-up tube 37,

A partially reflecting mirror 39 is provided between the lens 35 and the pick-up tube 37, and is positioned to reflect an image of the radar indicator tube 3 to the pick-up tube 3'5. A lens 4| is provided to focus the radar image on the pickup tube target. The mirror 39 is preferably of the dichr'o'ic type, designed to reflect the light from the tube 3 (for example, blue) and transmit the light passing through the inscriptions on the writing surface.

In the system shown in Fig'ure 2, the map is on a separate transparency like a lantern slide 43, illuminated by a source 45 and reflected by a partially reflecting mirror 41 disposed between the radar display tube 3 and the lens 4|. The mirror 41 may be neutral (i.e. not color selective) and designed to transmit for example percent and reflect 30 percent. It is also pos- 'sible that the colors of the radar oscilloscope, the map, and the writing surface could be selected so that both mirrors 41 and 39 could be dichroic, the mirror 41 transmitting the color of the tube 3 and reflecting that of the map, while the mirror 39 reflects both of said colors but transmits the color of the writing surface.

In the operation of the system of Figure 2, the composite television picture is displayed, as in the system of Figure 1, upon the monitor tube I 5. As the operator moves the pointer 2! over the screen of the monitor tube, the stylus 23 removes opaque material from the writing surface 29, producing bright line's upon the television picture. Thus the operator can see what he is doing and move the stylus properly without difficulty. If desirable, the stylus 23 can carry a small light source at its point to show its position with respect to the televisionpicture before it is lowered to the writing surface.

In the system shown in Figure 3, the monitor tube 15 and the map 19 are superimposed optically by means of a partially reflecting mirror 5!, for viewing by an observer at the point 0. The mirror 5| also serves to reflect the map l9 to a mirror I1, arranged like the correspondingly designated mirror in the system of Figure 1. The remainder of the system of Figure 3 is like that of Figure 1.

The phosphor on the monitor oscilloscope i5 is made of some color, such as orange, which will be substantially reflected by the mirror 5!. The illumination of the map 19 must contain some color which will be transmitted by the mirror 5|, as well as some color which will be reflected to and by the mirror 11.

Substantially all of the light from the monitor oscilloscope I5 is reflected to the observation point 0, where it appears to come from the plane of the writing surface support IS. The writing surface may be viewed through the mirror 5!. The mirror I? operates as in Figure 1 to superimpose the writing surface upon the P. P. I. display appearing on the tube 3. It will be apparent without further discussion or illustration that the map and/or writing surface shown in Figure 2 could be used in the system of Figure 3 by a combination of the two mirror arrangements.

I claim as my invention:

1. A television transmitting system comprising radio locator means including a cathode ray indicator havin a fluorescent screen for producing a luminous display representing information as to the positions of mobile craft in an operating zone, means comprising a lamina carrying a map-like facsimile representing features of said zone and a source of light for flooding said lamina to produce a second luminous display, said fluorescent screen having relatively high efliciency and emitting light of a particular predetermined color whereby said first-mentioned display is predominantly of said particular color, said source and said lamina being of such type and so arranged that said second luminous display includes a substantial amount of light of a different color, a television camera having a photo-sensitive image-receiving area which is responsive to both of said colors, means for optically superimposing said first-mentioned display upon said second display on said imagereceiving surface, said last-mentioned means including a dichroic mirror of such a type that in one of its two properties of respectively transmitting and reflecting impinging light it is adapted to transfer a large percentage of impinging light of said particular color, the mirror being arranged in said last-mentioned means to intercept light from said first-mentioned display and to transfer to said image-receiving surface a large percentage thereof and also to intercept and transmit to said surface some light from said second display.

2. A television transmitting system comprising radio locator means including a cathode ray indicator having a fluorescent screen for producing a luminous display representing information as to the positions of mobile craft in an operating zone, means comprising a lamina carrying a map-like facsimile representing features of said zone and a source of light for flooding said lamina to produce a second luminous display, said fluorescent screen having relatively high efficiency and emitting light of a particular predetermined color whereby said first-mom tioned display is predominantly of said particular color, said source and said lamina being of such type and so arranged that said second luminous display includes a substantial amount of a color contrasting with that of said first display, a television camera having a photosensitive image-receiving area which is responsive to both of said colors, means for optically superimposing said first display upon said second display on said image-receiving surface, said last-mentioned means including a dichroic mirror adapted to transmit a large percentage of light of one of said colors and to reflect a large percentage of light of the other, the mirror being arranged in said last-mentioned means to intercept light from each of said displays and to transfer a large percentage of it to said image receiving surface.

HORACE CLIFFORD ALLEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,927,900 Philpott Sept. 26, 1933 2,027,527 Hammond Jan. 14, 1936 2,122,918 Phinney July 5, 1938 2,150,551 Kemp Mar. 14, 1939 2,262,942 Jones Nov. 18, 1941 2,275,026 Bedford Mar. 3, 1942 2,298,476 Goldsmith Oct. 13, 1942 2,307,029 Elm Jan. 5, 1943 2,352,777 Douden July 4, 1944 2,405,252 Goldsmith Aug. 6, 1946 FOREIGN PATENTS Number Country Date 295,210 Great Britain Aug. 9, 1928 323,818 Great Britain Jan. 13, 1930 326,603 Great Britain Mar. 20, 1930 

